Eaton's Reply to Differential Fluid Questions

[TxDoc]

"GM introduced the new body style in 1998.  At the same time they upgraded

the differential and changed to a synthetic lube.   The G80 is specifically

designed to give ultimate performance with this lube, and the lube contains

special additives that help reduce slip stick that occurs between the

clutches. the GM synthetic lube typically runs about 100+ degrees cooler

than mineral base lube, which is better if you do allot of towing or heavy

hauling. I would recommend that you stay with the GM synthetic, not Mobil 1.

If you don't tow or haul you could use the pre 1998 mineral lube  without

degrading performance of the differential. this would be a cheaper option

but require more lube changes. "

 

 "Axle tolerances of the 1/2 ton trucks are very tight. The recommended

procedure was to change lube after 500 miles of heavy towing, which would is

considered a break in period.  This breaking period generates high heat

conditions in the axle which was found to degrade the synthetic beyond the

point of mineral lube.   After the 500 mile lube change, the axle is broke

in and does not generate the high heat.  If you use GM synthetic after the

break-in period, it can be considered "lube for life", although some say to

change it at 40,000 - 50,000 mile intervals."

 

 "If you don't tow, don't worry about the oil change as it a waste of money."

 

 

"If your truck is pre 1998 or the old style, it comes with mineral lube.  IN

that case you need to stay with mineral because the seals are designed to

work with it.  If you changed from mineral to synthetic you'll cause your

seals to swell and eventually leak.   It's ok to go from synthetic to

mineral because you won't cause swelling.    many of your stop leak

chemicals effect seals in this manner, resulting in a short term fix but a

long term problem."